In 1211, the Latins were in control of Constantinople, while Greek princelings ruled states in Epiros and Nikaia. The self-proclaimed emperor of Nikaia was Theodoros Laskaris, the son-in-law of the last Angeloi emperor Alexios III, who along with his wife and children had escaped the fall of Constantinople in 1204 by the skin of their teeth.
As for Alexios III Angelos, he had abandoned his city shortly before the capture of Constantinople, and spent the next few years wandering hither and dither, even being captured and imprisoned by the Latin lord Bonifazio of Montferrat. His cousin Mikhael of Epiros ransomed him, and Alexios III got in contact with Gıyaseddin Keyhüsrev, the Seljuk sultan.
Alexios III and Keyhüsrev went way back. Keyhüsrev had been deposed and driven from Seljuk territory by his brother, and come as an exile to Constantinople during the reign of Alexios III. The emperor welcomed him as the son he'd never had, even going through a sort of adoption/baptismal ceremony with the young man. According to Choniates, Keyhüsrev called Alexios III's daughters, including Laskaris' wife Anna, his "sisters". After the fall of Constantinople, Keyhüsrev's brother died and he was able to return to power in the Seljuk state.
In 1211, Keyhüsrev took up Alexios III's cause, and their first act was to turn against Theodoros Laskaris. When Laskaris refused to step down as 'emperor', Keyhüsrev's forces invaded Nikaian territory.
OTL, Laskaris killed Keyhüsrev on the field of battle, and took Alexios III prisoner. In this timeline, Keyhüsrev slays Theodoros Laskaris and the Seljuks are victorious.
What happens next?